Direct-current arc-welding generator



y 1942- J. TYRNER 2,291,008

- DIRECT-CURRENT ARC-WELDING GENERATOR 7 Filed Dec. 6, 1939 4 Sheets-Sheet 1 INVENT OR.

ATTORNEY? July 2 9 v J. TYRNER 2,291,008

DIRECT-CURRENT ARC-WELDING" GENERATOR Filed Dec. 6, 1939 4 Sheets-Sheet? y 942. I a J. TYRNER 2,291,008

DIRECT-CURRENT ARC-WELDING GENERATOR Filed Dec. 6, 1939 4 Sheets-Sheet s INVENT OR.

ATTORNEYS Patented 'July 28, 1942 nmncr-cuaaau'r ARC-WELDING oauam'roa Joseph Tyrner, Englewood, N. 1., auignor to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York 'Appiication December 6,1939, Serial No. 307,7

Claims.

The present invention relates to direct-current arc welding and has particular reference to generators for use in this art of the type employing a series-field winding for self-regulation.

An object of the invention is to provide a generator of the character mentioned having improved transient characteristics.

In accordance with the invention, self-regulation is effected by the use of a series-field winding of cumulative action with respect to the main field winding. A field magnet frame is employed which provides a magnetic path for leakage fiux outside the armature in addition to the usual magnetic. path for working flux through the armature, such frame being constructed to include a saturated portion common to each of the two paths. The main field winding interlinks with each of the two paths, while the series-- field winding interlinks only with the leakage flux path. With the series-field winding supporting the main field winding in the leakage flux path, self-regulation is obtained with improved transient characteristics.

The foregoing generator construction permits the inclusion of various other features of construction with additional advantages. By controlling the reluctance of the leakage flux path,

- a convenient means is provided for varying the operating current output. By taking the excitation for'the'main field winding from an auxiliary brush and the load brush following it in the direction of armature rotation, the means efi'ecting the operating current outputvariation is made to provide both higher and lower operating current output values. By the use of an auxiliary field winding of either cumulative action in the working fiux path or differential action in the leakage fiux path and of a type adapted to be supplied with open-circuit excitation, the operating current output may be varied by the aforementioned reluctance control without varying the open-circuit voltage, aside from which more economical production of the opencircuit voltage is obtained regardless of the means effecting the operating current output variation. By the use of an auxiliary series-field winding of cumulative action in the working fiux path, the limits of the operating current output variation may be controlled with reference to the degree of internal reactance'desired. These and other specific advantages of the invention will hereinafter become apparent in the detailed description of the drawings.

Figs. 1 to 6 are schematic views of two-pole to 9 are explanatory diagrams appertaining to external characteristics obtainable by the invention.

Each of the six machines illustrated comprisesa two-pole armature I of conventional type adapted to rotate between diametrically opposite poles 2 and 3. The upper pole 2 is of the Manchester type supported by side supporting cores 4 from the outer yoke 5 of the magnet frame, which includes an upper yoke extension 5a magnetically cooperating with the upper pole 2 through a regulating core 6 adapted by its inward and outward movement to vary the air gap formed between its lower surface and the upper surface of the upper pole 2. The cores 4 of each machine are of restricted cross-section resulting in their being magnetically fully saturated under'all operating conditions. As shown, the lower pole 3 may be of the usual type extending radially inwards from the lower yoke portion 5b magnetically'cooperating with each of the two poles 2 and 3.

Y In each machine, the armature i is equipped with clockwise rotation of the armature I as being required to cause the brushes 8 to have their respective polarities indicated.

machines embodying the invention, while Figs. 7

The field winding arrangement of each machine includesmain field coils 9 carried by the cores 4, and a series-field coil I 0 suitably supported in surrounding relation to the regulating core 6. The coils 9 produce working flux W through the armature, as well as leakage flux L through the controlled reluctance path provided by the regulating core 6. The series-field coil l0 contributes to the production of the leakage fiux L, in which respect it is wound to assist the coils 9. In each machine, the assumed directions of the two fluxes are such that north and south polarities are respectively produced in the two poles 2 and 3 by the working flux W, as is indicated by the usual symbols N and S.

As shown, each machine may include the usual interpole cores H disposed to align with the armature commutating zones, and the usual series coils i2 carried by the interpole cores II, it being understood that the coils I! should in the usual manner he woundto produce north and south polarities in the lnterpole cores ll respectively preceding the main poles of north and south polarities in the direction of armature rotation R.

The load brushes 8 of each machine are shown connected by conductors IS in series circuit relation to the series-field coil iii and interpole Still referring to Fig. 1, no current fiows on open-circuit through the series-field coil II, which is therefore ineffective in producing. the leakage fiux L. On the other hand, the coils I on open-circuit are effective in producing both the working fiux W and the leakage fiux L in relative amounts depending on the position of the regulating core 8. Under load conditions, the

series-field coil ll becomes excited by the load current and contributes more and more to the production of the leakage fiux L with increase of such current, the leakage fiux L finally attaining a maximum value on short-circuit. Because of saturation in the cores 4, substantially no the main field winding is not at all objectionable,

' but on the contrary decidedly beneficial.

Another factor contributing to improved transient characteristics in the generator construction of the invention is the saturated portion included in its field magnet frame. In the machine of Fig. 1, the sum of the two fiuxes W and L must at all times remain substantially constant because of saturation in the cores 4. This in itself is effective in varying the working fiux W inversely to the leakage fiux L in response to resistance change in the load circuit, and is therefore effective in limiting the amplitude of any abnormal change in the load current (developing from such resistance change) by the accompanying change in the generated voltage. It is clear that the saturated magnet frame portion included in the generator construction of the invention largely contributes to its improved tranchange in the sum of the two fiuxes W and L is produced by this increase in the leakage fiux L; but increase of the fiux produced through the leakage path by the series coil ll decreases by the same amount the working fiux through the armature produced by the main field coils I. Consequently, the coils I, although producing no more of the leakage fiux L under any load than on open-circuit, are caused under increasing load to produce less and less of the working fiux W. Since this is the only one of the two fiuxes W and L to generate voltage in the armature, it is apparent that the machine of Fig. 1 is characterized by a self-regulating drop in terminal voltage from open-circuit to short-circuit conditions, the

working fiux W finally attaining a short-circuit value merely in excess of zero to enable it to generate the slight terminal voltage required for short-circuit current fiow.

The principle of self-regulation described in connection with the machine of Fig. 1 results in greatly improved transient characteristics, as will now be explained.

Since the generator construction of the invention employs a series-field winding of cumulative actionwithrespecttothemainfieldwinding.the usual current surges accompanying the sudden resistance changes in welding operations are actually minimised by transformer action of the series-field winding on the main field winding. Inthemachineofl'ig. i,anysuddenincrease in theleakagefiuxLduetoresistancedecreasein the load circuit (increasing the excitation of the series-field winding ll) induces current in the mainfield'coils I of suchdirection asto decrease theworkingfiuxW; whileanysuddendecrease intheleakagefiuxLduetoresistanceinerease in the load circuit (decreasing the excitation of the series-field coil ll) induces current in the mainfieldcoilslofsuchdirectionastoincrease the working fiux W. Regardless of the nature of the resistance change in the load circuit, the machineof Pig. 1 thusoperates'to limitthemasnitude of any abnormal change in the load current (developing from such resistance change) by the accompanying change in the generated voltage. It is clear that the generator construction of the invention is one according to which transformer action of the series-field winding on sient characteristics.

Besides minimizing the usual current surges in welding operations, the generator construction of the invention results in rapid recovery incident to such surges. This is essentially due to the fact that either magnetic path provided by its field magnet frame may as the occasion arises draw fiux from the other. In the machine of Fig. 1, working fiux W is always available to become leakage fiux L in response to a resistance decrease in the load circuit (increasing the excitation of the series-field winding i0); while leakage fiux L is always available to become working fiux W in response to a resistance increase in the load circuit (decreasing the excitation of the series-field winding ll) Regardless of the nature of the resistance change in the load circuit, the machine of Fig. 1 thus readily responds to such resistance change, with the result that any abnormal change in the load current (developing from such resistance change) is quickly terminated. It is clear that the generator construction of the invention has transient characteristics which as a whole are excellent.

Again referring to Fig. 1, the regulating core 8 by its control of the gap 0 functions to vary the operating current output. This is evident from the fact that the short-circuit value of the load current required to take substantially all of the working fiux W out of the armature depends on the reluctance of the magnetic path for the leakage fiux L. An outward movement of the re lating core I increases the operating current output by increasing the gap 0, while an inward movement of the regulating core l decreases the operating current output by decreasing the gap 0. minimum operating current output being obtained with the reluhting core 0 in its innermost position of contact with the upper pole 2. While this reluctance control by the regulating core 8 affords a convenient means for varying the operating current output, it is understood that this variation may be effected in any other manner, as by a control of the turns of the series-field coil ll.

neferringtorimmthemainfieldcoilslin themachineofthisfigunareexcitedfromthe armature l by making use of its cross-mulletization by the load current, for which p r an auxiliary brush II is carried by the commutator I forusebetweentheloadbrushesl. Asahown. the armature l under load establishes cross-fiux A through each of its upper and lower halves.

The auxiliary brush ll maybe positionedtocowhich, condition the cross-flux A assists the working fiux W through the armature coils connected by the armature rotation to the load brush 8 employed. The auxiliary brush i9 is shown to be positioned to cooperate with the upper armature half, in which position the load brush 8 following it in the direction of armature rotation R is of positive polarity. Conductors 20 therefore connect the main field coils 9 across the auxiliary brush i9 and the load brush I of positive polarity; it being understood that a parallel connection of such coils across the same brushesr may in practice replace their series connection illustrated. Although the auxiliary brush i9 is shown positioned in electrical quadrature with the load brushes 8, it is evident that its usefulness is not limited to this particular position, from which it may depart considerably in practice. As positioned to cooperate with the upper armature half, the auxiliary brush I9 is obviously of negative polarity with respect to its associated brush 8 of positive polarity.

sun referring to Fig. 2, the exciting voltage" between the cooperating brushes I 9 and 8 is gen erated on open-circuit by the working flux W alone and under load by the working fiux W in conjunction with the cross-flux A. Under increasing load, the working fiux W decreases more and more to finally become practically zero on short-circuit, but this is compensated by the corresponding increase in the cross-fiux A, which finally becomes a maximum on short-circuit. From this it is apparent'that the main field coils 9 are supplied with proper excitation under all operating conditions.

In accordance with the invention. the exciting of the main field winding included in its generator construction in the manner described in connection with the machine of Fig. 2 has the advantage of much wider operating current output variation by the means employed for this purpose. In thisconnection it should be noted that the generator construction of the invention is one according to which substantially the only fiux produced in the armature on short-circuit is the cross-flux established by the armature itself. In the machine of Fig. 2, the short-circuit excitation of the main field coils 9 therefore varies substantially in direct proportion to the shortcircuitvalue of the load current as the operating current output is increased or decreased by the regulating core 6, which has the efiect to considerably increase the effectiveness of such core toward either of its limits of adjustment, the shortcircuit excitation of the main field coils 9 being considerably greater than, their open-circuit excitation for the highest operating current output setting and considerably less than their opencircuit excitation for the lowest operating current output setting. It is clear that the generator construction of the invention permits varying the operating current output over a range of much higher and lower values by its inclusion of the exciting means described in connection with the machine of Fig. 2.

Referring to Figs. 3 and 4, the lower pole 3 carries an auxiliary field coil 2| in the machine of Fig. 3 and an auxiliary field coil 22 in the ma chine of Fig. 4, each of these two machines being otherwise identical to the machine of Fig. 1. Each of the coils 2i and 22 is wound to assist the main field coils 9 in the production of the working flux W and is of a type adapted to contribute to such working flux production on short-circult. The coil 2i (Fig. 3) is a shunt-field coil shown connected as a short shunt by conductors 22 across the load brushes 8, while the coil 22 (Fig. 4) is a constantly excited coil shown connected in the series circuit of the conductors l8 across the source ll, it being understood that any circuit connection of the coil 2i (Fig. 3) adapting it to receive current from the load brushes 8 and any circuit connection of the coil 22 (Fig. 4) adapting it to receive current from the source I] may be used in practice. As noted, each of the coils 2| and 22 contributes to the production of the working fiux W without contributing to the leakage fiux L, which is the primary functionof these coils iirthe machines of Figs. 3 and 4.

In accordance with the invention, when the operating current output in its generator construction is varied by reluctance control of the leakage path outside the armature. as in the machines of Figs. 3 and 4, the use of an auxiliary field winding in the manner described in connection with these machines is of particular advantage because of its compensating efiect in connection with the undesirable variation in open-circuit voltage normally inherent in such operating current outputvariation, as will now be more particularly described by comparison of the machines of Figs. of Fig. 1.

In the machine of Fig. l, the open-circuit voltage necessarily decreases as the regulating core 6 is moved inwardly to decrease the operating current output, by which regulating core movement the main field coils 9 are rendered more effective in producing the leakag flux L and therefore less effective in producing the working fiux W. In the machines of Figs. 3 and 4, this condition can be fully corrected by proper design of their auxiliary field coils 2i and 22. Since these coils interlink with the path of the working flux W without interlinking with the path of the leakage flux L, they function through the upper yoke portion 5a to oppose the production of the leakage fiux L by the main field coils 9, as illustrated by the imaginary fiux F. Moreover, they increasingly oppose the production of the leakage fiux L in this manner with decreasing dis- 3 and 4 with the machine 'tance of the regulating core 6 from the upper age fiux L, the condition prevailing in the machine of Fig. l is fully corrected in the machines of Figs. 3 and 4, the working flux W produced by the main field coils 9 in conjunction with either one of the auxiliary field coils 2| and 22 and hence the voltage generated by such fiux being caused to have constant values throughout the range of operating current output variation provided by the regulating core 6.

Referring to Figs. '7 and 8, the lines Ea and Eb in. each ofthese figures can be regarded as schematically representing the limiting characteristics of terminal voltage against current output obtained by moving the regulating core 6 into its innermost 'and outermost positions in the machine of Fig. 1. These characteristics are seen to have unequal open-circuit voltage values Vi and V2, which causes them to meet theoretically at a point P on the left of the voltage axis. It can be proved that the distance d of such point from such axis depends on the reluctance opposing the production of the working flux W outside the cores 4 (substantially the reluctance through the armature between the poles 2 and 2) In the machines of Figs. 3 and 4, the coils 2| and 22 thus function to shift the point P toward the voltage axis by their diminishing action on the open-circuit drop of magnetic potential outside the cores 4, which is equivalent to a reduction in reluctance. In this manner, the point P can be shifted the whole distance d to the point P on the voltage axis, which merely requires that the open-circuit ampere-turns or the coils 2| and 22 be made strong enough to make such open-circuit drop of magnetic potential zero for any position of the regulating core 8. Assuming this condition to prevail in the machines of Figs. 3 and 4, the lines E and Ed schematically represent the corresponding limiting characteristics of the machine of Fig. 3, while the lines Ee and El schematically represent the corresponding limiting characteristics of the machine of Fig. 4. As noted, each of these machines raises each of the unequal open-circuit voltage values VI and V2 to the constant value P.

Still referring to Figs. 7 and 8, the characteristics E0 and Ed peculiar to the use of the shuntfield coil 2| have the same short-circuit current values SI and S2 as the characteristics Ea and Eb, while the characteristics Ee and E! peculiar to the use of th constantly excited coil 22 have short-circuit current values S3 and S4 greater than the values Si and S2 by th current value of the distance d. Therefore, the characteristics Ec and Ed slope more steeply than the characteristics Ee and E], which are parallel to the characteristics Ea and Eb. The line 11 in these figures indicates by its intersection with the various characteristics illustrated the corresponding operating current output values obtained. The operating current output value of the characteristics Ea and Eb are CI and C2, the operating current output values or the characteristics E0 and Ed are C3 and Cl, and the operating current output values of the characteristics Ee and E! are C5 and CB. As noted, each of the coils 2| and 22 functions to shift the range of operating current output variation normally obtained without its use to include higher operating current output values at the expense of the lower operating current output values, but the extent of this effect by the use Of the shunt-field coil 2| is slight as compared to its extent by the use a of the constantly excited coil 22. This together with the fact that the shunt-field "coil 2| provides for steeper characteristics makes the use of this coil more desirable than the constantly excited coil 22 in correcting for the condition represented by the characteristics Ea and Eb.

The use of the coils 2| and 22 should not be regarded as being restricted to the production of the constant open-circuit voltage value P. If desired, their open-circuit ampere-turn may be made strong enough to shift the point P even beyond the voltag axis, which provides for higher open-circuit voltage throughout the range of operating current output variation. This condition is illustrated in Fig. 9, it being for convenience assumed in this figure that the point P is shifted to the same point P" on the right of the voltage axis by each of the coils 2| and 22. The use of the shunt-field coil 2| results in limiting characteristics Egand Eh having opencircuit voltage values V2 and V4, while the use of the constantly excited coil 22 results in limiting characteristics El and E1 having open-circuit voltage values VI and V2. The four voltage values V2 to V8 all differ from one another, but

are all higher than the constant value P obtained in Figs. '1 and 8.

It should be noted that, when the condition illustrated in Fig. 9 is caused to prevail inthe machines of Figs. 3 and 4, the flux F is then actually produced on open-circuit, as well as under load until the point P" is reached. For any position of the regulating core 8. this flux has a maximum open-circuit value from which it decreases to zero at the instant of current passage through the point P". It is of the same direction as the working fiux W. which it therefore assists in generating the terminal voltage from open-circuit to the point P" for any position of the regulating core 8. Its open-circuit value increases with a resulting increase in open-circuit voltage as the regulating core I is moved inwardly to decrease the operating current output. which accounts for the open-circuit voltage values V2 and V5 being higher than the open-circuit voltage values V4 and VB.

As before, the characteristics Eu and Eh peculiar to the use of the shunt-field coil 2| have the same short-circuit current values BI and 82 as the characteristics Ea and Eb. On the other hand, the characteristics El and E1 peculiar to the use of the constantly excited coil 22 have still higher short-circuit current values 85 and SO by reason of their increased distance of parallel separation from the characteristics Ed and Eb. Therefore, the aforementioned desirability of employing the shunt-field coil 2| in preference to the constantly excited coil 22 is even greater in connection with the condition illustrated in Fig. 9. As noted, the shunt-field coil 2| provides for a higher range of open-circuit voltage values than the constantly excited coil 22, but this is merely due to the fact that each of these coils is made to shift the point P the same distance to the point P", which necessitates more opencircuit ampere-turns in the case of the shuntfield coil 2| than in the case of the constantly excited coil 22.

In accordance with the invention, the use in its generator construction of an auxiliary field winding of the type of either one of the coils 2| and 22 also results in more economical production of the open-circuit voltage, as is evident from the fact that the leakage flux L in the machines of Figs. 3 and 4 can be made zero on open-circuit, it being understood that this advantage is entirely independent of the operating current output varying means employed.

In connection with the machines of Figs. 3 and 4, it should be noted that the various effects provided by their respective coils 2| and 22 may also be obtained by the use of similar coils of differential action arranged to interlink with the path of the leakage flux L without interlinking with the path of the working flux W. as y suitably snpporting them with the series-field coil III in surrounding relation to the regulating core 6. While this possibility should be regarded as being included within the scope of the invention, the use of the cumulative coils 2| and 22 on the lower pole I has not only the advantage of greater convenience, but also the advantage of no inductive action with the series-field coil ll.

Itisunderstoodthatthemainfieldcoilslin the machines of Figs. 3 and 4 may be excited in the manner described in connection with the mehineofFlg.2. Ifdesired,thecoil22inthe machine of Fig. 4 may also be excited in this manner. the use of this excitation in oonnectim with this particular coil considerably diminishing rent. Thismachine is otherwise identical to the machine of Fig. l, the main field coils 9 again deriving their excitation from the independent source I I. As noted, the series-field coil 2t contributes to the production of the working flux W without contributing to the production of the leakage flux L, which condition is indispensable for its proper performance.

In accordance with the invention, the use of its generator construction of an auxiliary series- -field winding in the manner described in connection with the machine of Fig. 5 provides the advantage that both operating current output limits may be effectively controlled with reference to the degree of internal reactance desired. As well I known in the art, high internal reactance is desirable in welding generators because of its steadying effect on the welding arc. The usual series-field winding employed for self-regulation in such generators provides a convenient means for increasing their internal reactance, but it is often difficult, on the one hand, to increase their internal reactance in this manner to the extent desired without, on the other hand, unduly af-' fecting the range of operating current output variation desired. When the generator construction of the invention is made to include the auxiliary series-field winding described in connection with the machine of Fig. 5, any degree of internal reactance may be obtained in such generator construction without adverse effect on either of "its operating current output limits. This feature of the invention will now be more particularly described in connection with the machine of Fig. 5.

For any position of the regulating core 8, it can be shown that the short-circuit current delivered by the machine of Fig.5 is given by the following general formula:

Rg m in which K is a constant depending on the design of the machine, but independent of any other factor in the formula; R9 is the external reluctance to either of the saturated cores 4 opposing the production of the leakage'flux L; NI is the number of turns of the series-field coil In; N2 is the number of turns of the series-field coil 24; and a is a variable depending on the reluctance Ry.

For the innermost position of the regulating core 8, it can be shown that the variable a is the same increase of number, of turns in each of the series-field coils I I and It.

For the outermost position of the regulating core 6, it can be shown that the variable a is a maximum greater than unity. Let this maximum be greater than one by the quantity n. Formula 1 then becomes the following specific formula for the upper short-circuit current limit:

This third formula shows that the influence of the series-field coil 24 on the upper short-circuit current limit is multiplied. This means that a given increase in the number of turns of the series-field coil I0 requires a smaller increase in the number of turns of the series-field coil 24 to restore the upper short-circuit current limit.

It necessarily follows from the foregoing facts that, by properly increasing the number of turns in each of the series-field coils I0 and-24, the machine of Fig. 5 may have its internal reactance increased to any extent desired without adversely affecting either of its operating current output limits. Each of these limits is decreased by increasing the number of turns of the series-field coil ill, but increased by increasing the number of turns of the series-field coil 24. Actually, the use of the series-field coil 24 in the machine of Fig. 5 results in a widening of the range of operating current output variation provided by the regulating core 6, as a comparison of formulas 2 and 3 shows. in itself having no adverse effect on the limits of such widened range, which may be shifted at ii-(mu) K m'll to include either higher or lower operating.

current output values by proper choice of the ratio of the number of turns in the series-field coil 24 to the number of turns in the series-field coil it. It is clear that the series-field coil 24 functions in the machine of Fig. 5 as an effective control of its operating current output limits with reference to the. degree of internal reactance desired.

The use of the series-field coil 24 in the machine of Fig. 5 should not be regarded as being restricted to the reluctance control by the regulating core 6. Any other means for varying the operating current output may be employed with the same advantage of effective control of either limit of the operating current output variation by the series-field coil 24. In the absence of the reluctance control by the regulating core 8, however, there is no widening efiect produced by the series-field coil 24 on the range of operatin current output variation, the limits of which are each dependent on the difference in number of features of the invention described in connection with the machines of Figs. 2 to 4. When either v of the auxiliary field coils 2i and 22 of the machines of Figs. 3 and 4 is used in conjunction with the series-field coil 2 of the machine of Fig. 5, there is still further tendency toward improved transient characteristics by reason of transformer actioncf the series-field coil 24 on one or the other of the auxiliary field coils 2| and 22, as the case may be.

Referring to Fig. 6, the machine illustrated in this figure differs from any of the five others But this is a distinct advantage illustrated in that the main field coils l are shunt excited from the load brushes 8. As shown, conductors 2! connect these coils in this machine in series circuit relation to one another and in short shunt relation to the load brushes I, it being understood that any other circuit connection adapting them to be supplied with current from these brushes may be used in practice. The machine of Fig. 6 is otherwise identical to the machine of Fig. 1.

As well known in the art, the use of shunt excitation for the main field winding of welding generators is often difilcult. The generator construction of the invention is one the operation of which is not at all affected by the use of such excitation for its main field winding. This will now be more particularly described in connection with the machine of Fig. 6.

For any position of the regulating core 6, the excitation of the main field coils O in the machine of Fig. 6 decreases from a maximum on open-circuit to substantially zero on short-circuit. On the other hand, the excitation of the series-field coil l increases from zero on opencircuit to a maximum on short-circuit. Therefore, the variation in the excitation of the seriesfield coil in functions through the saturated cores 4 to compensate for the variation in the excitation of the main field coils 9. Moreover, as the regulating core 8 is moved in either direction of adjustment to vary the operating current output, the variation in the reluctance of the air gap 9 compensates for the short-circuit variation in the excitation of the series-field coil iii. In view of these facts it is apparent that the machine of Fig. 6, in spite of its use of shunt excitation for the main field coils 9, can be designed so that, for any position of the regulating core 8, the total flux produced through the saturated cores 4 has a substantially constant value from opencircuit to short-circuit conditions, which is the condition required for its proper operation.

The use of shunt excitation for the main field coils 9 in the machine of Fig. 6 should not be regarded as being restricted to the reluctance control by the regulating core 6, the tendency of the total fiux produced through the cores to remain constant under all operating conditions being independent of the means employed for varying the operating current output, which means functions in any case to maintain the short-circuit value of the leakage fiux L substantially constant. In fact, the use of shunt excitation for the main field coils l in the machine of Fig, 6 is possible in the absence of any means for varying the operating current output.

The machine of Fig. 6 may include any of the features of the invention described in connection with the machines of Figs. 3 to 5.

It now becomes apparent that there has been provided a direct-current generator construction for arc welding which provides for self-regulation with improved transient characteristics, but which may include various other constructional features with additional advantages, it being understood that the invention is not limited to its foregoing illustrative embodiments, but that it may be carried out in various other ways within the purview of the claims.

What is claimed is:

1. A direct-current generator for arc welding according to claim 5, provided with an auxiliary field coil cooperating with said first mentioned pole-piece and producing working magnetic fiux in the same direction as the working fiux produced through the armature by said main field coils.

2. A direct-current generator for arc welding according to claim 5, provided with an auxiliary field coil cooperating with said first mentioned pole-piece and producing working magnetic fiux in the same direction as the working fiux produced through the armature by said main field coils, said auxiliary field coil being connected to the brushes of said generator and said main field coils being constantly excited from an independent current source.

3. A direct-current generator for arc welding according to claim 5, provided with an auxiliary field coil cooperating with said first mentioned pole-piece and producing working magnetic fiux in the same direction as the working fiux produced through the armature by said main field coils, said auxiliary field coil and said main field coils being both constantly excited from an independent current source.

4. A direct-current generator for arc welding according to claim 5, provided with an auxiliary series field coil cooperating with said first mentioned pole-piece and producing working magnetic fiux in the same direction as the working flux produced through the armature by said main field coils.

5. A direct-current generator for arc welding, comprising a two-pole field magnet frame, a polepiece supported by said frame, another pole-piece located both physically and electrically diametrically opposite said first mentioned pole-piece and connected to said frame by supporting cores of such restricted cross-section that they are magnetically fully saturated under all operating conditions, a regulating core supported by said frame for movement toward and away from said second mentioned pole-piece, a two-pole armature arranged for rotation between said diametrically opposite pole-pieces, main field coils cooperating with and producing through said magnetically i'uliy saturated supporting cores working magnetic fiux passing from one polepiece to the other pole-piece through said armature and leakage flux passing through said regulating core, and a series winding cooperating with said regulating core and producing fiux only through said leakage fiux path and in the same direction as the leakage flux produced by said main field coils whereby increase of the fiux produced through the leakage path by said series winding decreases by the same amount the working fiux through the armature produced by said main field coils.

JOSEPH TYRNIR. 

